hi mam,let me tell you that in babies 1)is baby feeding well or any disturbances like disinterest in feeding,excessive crying.
2)is baby active that is actively moving hands and legs,sleeping well,cooing,responding to mother's touch and so on.
3)how is the weight gain.recommended weight gain is first 6months,140-200gms per week.doubles the birth weight by 5months.
4)is there any abdominal tightness or distention,excessive crying.
5)green stools are not abnormal especially in formula fed babies.so dont worry.
6)just observe till how many days your baby wont poop without giving lactulose.
7)check if the breast milk is adequate.also the entire feeding formula ie;breast milk and formula combinedly must be adequate to satisfy his hunger.the factors that indicate adequacy of feeding are baby sleeps well and doesnt cry for feed within half an hour of feeding,we can assume that hunger is satisfied.
8)lastly in hypothyroidism also infants constipate but it is associated with other symptoms like sluggish baby,feeding difficulties,umbilical hernia,poor cry etc.
so,just check for the above factors and if everything is normal,you can assume that his bowel habits now are not abnormal.let me also assure you that bowel habits will become regular once he reaches 6 months of age and complimentary feed starts.trust me,even my baby used not to pee for >15 days until 4 months of age.later she started every 4-5 days and now she is regular.just relax and dont overload him with lactulose.as its not any abnormality or pathology,you can just wait and watch.hope my answer allays your apprehension.take care of your baby.i pray god that your baby thrives well.thank you.any further queries are welcome with pleasure.bye.